Condensation of the antitumor antibiotic epirubicin with oxidized chitosan provided a new conjugated antibiotic. The resultant compound was characterized by IR and UV-Visspectra with support the conjugate structure. The amount of epirubicin bound to the matrix was 22.5 % or 315 epirubicin residues. The biological activity of epirubicin-chitosan conjugate showed an antibacterial action against Bacillus Subtilis AT 6633 on the level of the initial antibiotic. The ascetic form of lymphocytic leukemia P 388 and lymphoid leukemia L1210 (transplantation dose 10 6 tumor cells) in hybrid mice BDF 1 was used as leukemic model. Antileukemic activity of the studied conjugate was found with a clear " dose-effect" correlation. The criterion "increase of live span" is maximally 342.1 % in P338 and 371.5 % in L1210 for the conjugate in comparation with maximally 179.0 % in P388 and 197.2 % in L1210 for the free epirubicin. The conjugate showed lower toxicity and higher therapeutic index.